Exploring, drilling, completing, and operating hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. In recognition of these expenses, added emphasis has been placed on well access, monitoring and management throughout the productive life of the well. That is to say, from a cost standpoint, an increased focus on ready access to well information and/or more efficient interventions have played key roles in maximizing overall returns from the completed well. By the same token, added emphasis on completions efficiencies and operator safety may also play a critical role in maximizing returns. That is, ensuring safety and enhancing efficiencies over the course of well testing, hardware installation and other standard completions tasks may also ultimately improve well operations and returns.
Well completions operations do generally include a variety of features and installations with enhanced safety and efficiencies in mind. For example, a blowout preventor (BOP) is generally installed at the well head in advance of the myriad of downhole hardware to follow. Thus, a safe and efficient workable interface to downhole pressures and overall well control may be provided. However, added measures may be called for where the well is of an offshore variety. That is, in such circumstances control at the seabed is maintained so as to avoid uncontrolled pressure issues rising to the offshore platform several hundred feet above.
One of the common concerns in the offshore environments in terms of maintaining well control at the seabed relates to challenges of heave and other natural motions of a floating vessel platform. That is, in most offshore circumstances, the well head, BOP and other equipment are found secured to the seabed at the well site. A tubular riser provides cased route of access from BOP all the way up to the floating vessel. However, also secured to the seabed equipment and running up through the riser is a landing string for providing controlled work access to the well. The landing string is of generally rigid construction configured with a host of tools directed at testing, producing or otherwise supporting interventional access to the well. As a result, the string is prone to being damaged in the event of large sways or heaving of the floating offshore platform.
Unfortunately, damage to the tubular landing string while the well is flowing may result in an uncontrolled release of hydrocarbons from the well. That is, a breach in the tubular landing string which draws from the well will likely result in production from the well leaking into the surrounding riser. Making matters worse, the riser extends all the way up to the platform as indicated above. Thus, uncontrolled hydrocarbon production is likely to reach the platform. Setting aside damaged equipment and clean-up costs, this breach may present catastrophic consequences in terms of operator safety.
In order to help avoid such catastrophic consequences, efforts are often undertaken to help minimize the amount of heave or motion-related stress to which the work string is subjected. For example, the string may be managed from the floor of the platform by way of an Active Heave Draw (AHD) system. Such a system may operate by way of rig-based suspension of equipment that is configured to modulate elevation in concert with potential shifting elevation of the floating platform. Thus, as the platform rises or falls, the system may work with excess cabling and hydraulics to responsively maintain a steady level of the work string.
Unfortunately, AHD systems of the type referenced rely on active maneuvering of equipment components in order to minimize the effects of heave on the work string. For example, a sufficient power source, motor and electronics operate in a coordinated real-time fashion to compensate for the potential shifting elevation of the platform. Accordingly, in order for the system to remain effective, each of these components must also remain continuously functional. Stated another way, even so much as a temporary freeze-up of the software or electronics governing the system may result in a lock-up of the entire system. When this occurs, compensation for potential heaves of the platform relative the work string is lost, thereby leaving the string subject to potential over pull and breach as noted above.
The problems of potential breach in the work string are often exacerbated where the floating platform is in a relatively shallow environment. For example, where the water depth is under about 1,000 feet, a single foot of heave may result in damage or breaking of the string if no compensation is available. By way of comparison, the same amount of heave may result in no measurable damage where the string is afforded the stretch that's inherent with running several thousand feet before reaching the equipment at the sea bed. Ultimately, this means that in the shallower water environment, operators are more prone to having to manage a breach in the case of lost active compensation and are afforded less time to deal with such a possibility. That is, in shallower waters, uncontrolled hydrocarbons may reach the platform in a matter of seconds.